....In the Johnson County, Iowa mask study:
"Among the limitations to this study is that many persons could not be contacted or declined to cooperate with public health investigations. There are almost certainly substantial differences between case-patients and contacts that we were able to interview and those who declined to provide information or were unable to be reached. In addition, all of the data, with the exception of test results, were self-reported by either contacts or case-patients. Self-reported data can be unreliable. During investigations, case-patients may have had an incentive to provide false information to prevent friends, co-workers, or classmates from quarantining; or they may have demonstrated response bias by telling interviewers what they thought we wanted to hear. Although bias cannot be ruled out, we believe that persons who cooperate with public health investigations are more likely to provide accurate and honest information and to follow other public health guidance, such as social distancing and mask use"
